It’s a quiet sunday morning when we roll into Weifang city, in China’s Shandong province, to interview local food producers, but our hosts are unperturbed. The export scandals are still months away, and the government is happy to show Western journalists the glories of China’s rapidly evolving food system. Within an hour, my interpreter and I are being escorted through the city’s newest showcase—a duck-processing plant where a shift of workers had been brought in and several thousand ducks dispatched—so that I can witness China’s most recent great step forward. And it is impressive. In huge, spotless rooms, rows of workers in clean-suits and hairnets are swiftly and methodically disassembling birds on a mechanical conveyor at a rate of 3,100 an hour. By tomorrow, these ducks will be bound for supermarkets in Beijing, to be snapped up by upscale shoppers as quickly as they can be put in the meat case.

China’s new meat proficiency goes beyond duck. Under the potent combination of industrialization, meat science, and rising wealth, meat production here is soaring—and so is consumption. Per capita intake of poultry, pork, fish, and even beef has more than tripled since 1970—a radical change in a nation long thought to have an almost philosophical preference for veggies over meat. “The Chinese have always regarded animal foods as better” than vegetables or grains, assures Yang Xiao Guang, of the China Nutrition Association. “We just had no money to buy them.”

The consequences of China’s new carnivorism have been enormous. Thanks in part to the meatier diet, the number of people suffering physical stunting has fallen from three in 10 in 1980 to half as many today. But because meat is so calorie-dense, rising consumption is contributing to an obesity epidemic that afflicts 100 million Chinese. The production process has itself brought a slew of complications. Rivers of sewage from China’s new “concentrated animal feeding operations,” or CAFOs, overwhelm local treatment facilities. Public health experts are increasingly worried about avian flu, whose epicenter is Asian poultry. And because factory-raised livestock need so much feed—it takes 4.5 kilograms of feed to make a kilogram of poultry meat and 20 kilograms of feed to make a kilogram of beef—China’s yen for meat is jacking up grain prices globally. In fact, because Chinese farmland is already so scarce, and because decades of industrialized agricultural have unleashed huge ecological problems (from chemical runoff to groundwater depletion), China has turned increasingly to imported feed—effectively pushing the “external” costs of its meat revolution onto farms in the United States, Argentina, and elsewhere.

And this is just the beginning. By 2030, China’s per capita meat consumption is expected to hit 50 kilograms, equal to neighboring Taiwan. Granted, that’s still barely half the levels projected in wealthy nations like the United States, but because China will have 1.6 billion consumers by then, the impact of this relatively modest increase will be extraordinary. Even now, China’s meat mania is implicated in everything from deforestation in Brazil to food-price inflation in Africa, and most resources specialists expect that this nutritional domino effect will only intensify. “I cannot imagine what the world will look like when China is as wealthy as Taiwan,” Tian Weiming, one of China’s top food security experts, told me. “It will be very different.”

In crucial ways, China’s meat revolution offers a preview of one of humankind’s most complex resource challenges. Over the next half century, global food demand, especially for meat, will rise dramatically—because population is rising and because most of the roughly 4 billion newcomers will be in the developing world, which is still catching up with Western dietary practices. By 2050, according to the United Nations’ Food and Agriculture Organization (FAO), worldwide meat consumption will reach nearly half a billion tons a year, more than twice the current level. And yet, no one has any idea how, or even if, the world can support that volume. Quite aside from issues of obesity or sewage, world farmers would need to grow another one billion tons of feed each year by mid-century—and this from an agricultural system already staggering under the impacts of declining acreage, water scarcity, climate change, and soaring energy costs. To be sure, all food production, like all economic activity, affects the natural systems on which life ultimately depends. But because meat represents such a concentrated use of resources, it has now forced a debate over the future of food—a debate that is beginning to reveal the flaws in an economic model premised on endless growth.

In a strange way, such bleak forecasts bring a welcome clarity to a discussion long confined to the margins of society. For decades, anyone who argued that humans should be eating less meat, or none at all, did so largely on moral grounds such as animal rights, or for religious reasons—arguments that the rest of society was free to ignore. True, one could make a science-based case for eating less meat, especially the fatty meat that comes from grain-fed livestock. Yet if people wanted to clog their arteries, the damage came at one’s own expense. Now the idea that meat-eating is purely an individual choice, and the costs affect only the individual, has been blown wide open. Just as chuffing on Marlboros or driving a gas-guzzling SUV—as Michael Specter recently put it—have become the modern day equivalent of wearing a scarlet letter, so too has meat-eating graduated from the category of lifestyle choice to that of collective responsibility.

What’s more, it’s clear that the question of how much meat we can or should eat cannot be resolved without a more global scientific approach. As we have with cigarette smoking and automobile preference—things that were once regarded as personal choices but whose societal costs are now precisely quantified—we now need to use science to essentially recalibrate our moral compasses when it comes to meat. What are meat’s true “external” costs? How much meat can we sustainably produce, in the context of a warming climate and dwindling resources? And how rapidly does our meatcentric food economy need to change? These aren’t easy questions. But just as science has shed light on other complex lifestyle issues, it must now offer a new and more pragmatic vision for the future of meat.

If science has shown us why we should be eating less meat, science has also shown why most of us will fight like hell to keep eating it: Humans love meat. Although scientists have found little evidence of a hard-wired craving for the specific taste of animal foods (other than an inclination toward fats), we do know that meat has played a central role in human evolution and that its presence in the human diet has had an extraordinary impact on everything from brain size to energy levels.

We know, for example, that around 3 million years ago, climate change forced a largely vegetarian ancestor, Australopithecus, to move from the forest to the open savannah, which offered fewer plant foods, but more prey. We know that our ancestors adapted—first by scavenging and later by hunting, and that by 500,000 years ago, a more recent ancestor, Homo erectus, was getting nearly two-thirds of her calories from meat.

Initially, this dietary shift to meat was purely pragmatic: All creatures adopt feeding strategies that yield the most calories for the least effort, and meat, which is more energy-dense and easier to digest than plants, was probably the most expeditious way for our ancestors to cope with the loss of their old herbivorous menu. But meat did more than just replace plant calories. Because meat offers more caloric bang for the buck than plants do, our ancestors could consume more calories more easily. These were better calories too, that converted more readily than those from plants into human protein—which meant that our ancestors’ rising meat intake was paralleled by an increase in body size. Whereas Australopithecus was just four feet tall, Erectus stood six feet and was much stronger. Also, Erectus’ skull was a third larger, and its brain vastly more developed—an adaptation, according most experts, also related to the meatier diet: Brains thrive on the long chain fatty acids, Omega 3 and Omega 6, that are abundant in animal fats and soft tissues.

Meat provided other evolutionary advantages. The brain is what’s known as “expensive tissue,” requiring many calories to fuel all the neurochemical activity. Bigger brains, not surprisingly, need more fuel, which is why in most species a big brain correlates with a big body that houses a large gut. But humans were different. In the millions of years between Australopithecus and Erectus, our brain size nearly tripled, yet our body size barely doubled, meaning we were somehow feeding a massive brain with a relatively small set of body organs. How? The answer, again, was likely meat. As our ancestors ate more meat and fewer plants, over time their guts shrank to about 60 percent the size of that in other primates—a critical development, as digestive systems themselves consume lots of calories, and having a smaller gut meant more available nutrition for our larger brains.

This is not a claim for dietary determinism: Meat didn’t “make” us human. Many factors, interacting in complex ways, spurred changes in our ancestors’ physiology that ultimately produced modern humans. But it’s also clear that without more animal foods, our bodies and brains couldn’t have gotten larger. And without those bigger bodies and brains, we couldn’t have become the intelligent, tool-using, highly effective hunters who were able to spread so quickly from Africa to the Middle East, Asia, and finally Europe. Even though humans are no longer under such intense evolutionary pressure, meat’s historic role in our development suggests that our modern cravings are more complex than many of us realize, and may well be much harder to curb.